1. Field of the Invention
This invention concerns a method for patterning an optical device for integrated circuits (optical IC), and an optical device for optical IC fabricated by this method.
2. Description of the Prior Art
In the prior art, methods exist for patterning optical devices for optical IC wherein an interference pattern is traced out directly by an EB (electron beam) or laser beam. Other methods are also known wherein a mask with an interference pattern is first prepared by tracing out a pattern directly on film using an EB or laser, and the pattern is then transferred to an optical substrate.
These conventional patterning methods however suffered from the inherent disadvantage that they required developing or other processing, and it was therefore difficult to obtain patterns wherein the pitch of the interference fringes was greater than 500 lines/mm expressed in terms of spatial frequency. In addition, it was difficult to form interference patterns of large surface area on the optical substrate, and furthermore the apparatus used in the conventional method used for patterning optical devices for optical IC was costly.
Further, as digitization was applied in manufacturing the optical devices for optical IC by the aforesaid conventional patterning method, diffracted light of unnecessary orders and quantization noise were produced, and the diffraction efficiency was also low.